Field of the Art
The present invention relates to technology for improving granulometric property, i.e. flowing characteristic, of granular propylene copolymers which are called propylene block copolymers.
Recently, it has become popular to produce propylene block copolymers comprising a resinous segment of polypropylene and an elastomeric segment of an ethylene-propylene copolymer by gas-phase polymerization, and the use of such block copolymers has been increased in automobile industries for manufacturing, in particular, bumpers, inner panels, outer sheeting and the like.
Such block copolymers may, however, have some drawbacks such that higher the content of elastomeric block is, increased will be the stickiness of polymer particles resulting in poor flowing characteristics whereby commercial value of product will be reduced and a problem will be posed upon transportation and storage of the product polymer.
Increase in the stickiness of polymer particles will invite adherence of polymer in a polymerization vessel, especially in a case of gas phase polymerization, whereby stable polymerization operation will often be impaired.